Chemical vapor deposition (or CVD) method has been used in the deposition of silicon dioxide films on semiconductor substrates. In this method, a gas containing the structural elements of the film material to be formed is fed into a chamber, followed by heating of the gas to induce a chemical reaction to deposit the desired film on the semiconductor substrate. In a conventional CVD method, a silicon dioxide film is deposited by the chemical reaction between silane (SiH.sub.4) and oxygen. This method enables the formation of a silicon dioxide film at a relatively low temperature.
The conventional CVD method of depositing silicon dioxide films by using silane and other reactant gases causes a step coverage problem, i.e., failure of coverage of the steep step portion in an advanced semiconductor element configuration by a film of uniform thickness. Others have attempted to solve this step coverage problem by utilizing a reactant of tetra-ethoxy-ortho-silicate. TEOS has better coverage characteristics than silane, however, TEOS must be used at high reaction temperatures due to its low reactivity. Attempts have been made to increase the reactivity of TEOS by means of plasma formation such that the reaction can be carried out at a lower temperature. Attempts have also been made to use ozone which has a higher reactivity than oxygen.
A problem arises when TEOS is used to replace silane in order to improve the step coverage. Conventional CVD equipment such as atmospheric-pressure CVD, reduced-pressure CVD, and plasma CVD cannot be used due to the fact that TEOS must be processed at a high temperature.
Additional problems occur when plasma is used to enable the use of TEOS in a low temperature CVD process because the intermediate reactant of tetra-hydroxy-silicon (Si(OH).sub.4) has a short lifetime. As a consequence, silicon dioxide with a cross-linked configuration is already formed before it flows into the grooves of the step portion and thus improvement of the step coverage cannot be realized.
When ozone is used to replace oxygen, although the step coverage is improved, the quality of the entire silicon dioxide film deposited on the substrate depends significantly on the ozone concentration. When ozone is generated by electrical discharge in oxygen, it decomposes to oxygen easily and hence the stability of the concentration is poor. As a result, it is very difficult to feed ozone at a high concentration into the reaction chamber. In addition, in the high-energy discharge process for generating ozone, undesirable metal impurities may be blended and particles may be generated.
Furthermore, in a conventional chemical vapor deposition, the process must be performed in two stages. In the first stage, an organic solvent containing the structural elements of the film is used to coat the substrate. In the second stage, heating is performed such that the film is formed on the substrate. When the deposition of a thick film is desired, the two stage operation must be performed repeatably. It is difficult to maintain a high degree of uniformity for a large-diameter semiconductor substrate used in present-day semiconductor manufacturing. This is a significant disadvantage which affects quality and yield of production.
It is therefore an object of the present invention to provide a novel method of depositing silicon dioxide films on a semiconductor substrate by a chemical vapor deposition technique without the shortcomings of the prior art methods.
It is another object of the present invention to provide a novel method of depositing silicon dioxide films on semiconductor substrates by a chemical vapor deposition technique such that conventional CVD equipment can be used.
It is yet another object of the present invention to provide a novel method of depositing silicon dioxide films on semiconductor substrates by a chemical vapor deposition technique such that the frequently occurring step coverage problem in an advanced semiconductor manufacturing process can be avoided.
It is a further object of the present invention to provide a novel method of depositing silicon dioxide films on semiconductor substrates by a chemical vapor deposition technique in which a mixture of reactant gases of tetra-ethoxy-ortho-silicate and activated oxygen are used in a carrier gas of oxygen.